To provide accurate printing of images, multicolor digital marking systems need to maintain adequate color to color registration. In systems that utilize an elongate image receiving surface, such as a paper web or a belt, the receiving surface reaches a first marking station where a marking material of a first color is applied to the surface, e.g., by firing ink jets, exposing an image on a photoconductive material, or applying toner particles to a selectively imaged photoconductive member. The receiving surface then moves on to a second marking station, where an image or marking material of a second color is applied, and so forth, depending on the number of colors.
Precise control of the timing of actuation of the marking stations is necessary so that the separate single color images deposited onto the web by the different print heads are precisely overlaid, or registered, on the web in order to produce the desired output color image. A continuous web, such as a length of paper or photoreceptor belt, however, may be a stretchable medium. Therefore, variations in the speed of the web at different locations in the web can cause the web to stretch or change length. Web stretch can affect the time at which a specific portion of the web reaches a marking station which in turn may cause a particular marking station to apply marking material at the wrong location on the web resulting in image registration errors.
Misregistration of images on the web may also result from other factors such as thermal expansion, mechanical vibrations, and other sources of disturbances on the machine components that may alter marking station positions or angles of incidence relative to the web. Slight deviations in position or angle of incidence from manufactured settings may cause marking material to be applied to the web by a marking station too early or too late relative to marking material applied by other marking stations resulting in process direction registration errors.